Stabilized amplifier



April 3, 1951 A. B. ANDERSON 2,547,107

STABILIZED AMPLIFIER Filed Sept. 18, 1947 3 Sheets-Sheet 1 FIG.

INPUT nvvmvron A. 8. ANDERSON ATTORNEY April 3, 1951 A. B. ANDERSON2,547,107

STABILIZED AMPLIFIER Filed Sept. 18, 1947 3 Sheets-Sheet 2 FIG. 3

42 \C INPUT {3 INPUT MAN 2 l r 7 I 3-20 :21 I] W /N|/E/VTO/? y A. B.ANDERSON ATTORNEY April 3, 19511 A. B. ANDERSON 2,547,107

STABILIZED AMPLIFIER v Filed Sept. 18, 1947 3 Sheets-Sheet 5 4 lNPUTNO.-/

L /NPUTNO.2

INVENTOR By A. 9. ANDERSON A T TOPNEV Patented Apr. 3, 1951 STABILIZEDAMPLIFIER Attell B. Anderson, East Orange, N. J., assignor to BellTelephone Laboratories, Incorporated, New York, N. Y., a corporation ofNew York Application September 18, 1947, Serial No. 774,855

8 Claims. (01. 179171) This invention relates to direct currentamplifiers, and particularly to means for compensating for variations inthe cathode activity of the amplifier tubes in such amplifiers.

The object of the invention is mean for compensating for variations inthe cathode activity of the amplifier tubes used in a direct currentamplifier without interrupting, or interfering with, the operation ofthe amplifier.

A feature of the invention is means for intermittently measuring thecathode activity of an amplifier tube, and manually adjustable means forcompensating for variations in the cathode activity.

, While the invention is of particular utility in connection with directcurrent amplifiers, it is not limited to this use but may be used tocompensate for variations in the cathode activity of any electrondischarge device. The compensation is mainly effective for variations incathode activity, but will also compensate for other variations in theoperating characteristics of the device.

In a known system for compensating for changes in cathode activity, atwo-section vacuum tube, having a cathode common to both sections, isused. A common coupling resistor is connected in the commoncathode-anode path of the two sections, and means are provided foradjustably biasing the control grid of the compensating section of thetube. The anode current of the working section of the tube is measured,and the bias on the grid of the compensating section adjusted until thisanode current has a desired value. In order, later, to check thisadjustment, the operation of the working section must be interrupted, tomeasure and readjust the anode current.

In accordance with one embodiment of the present invention, atwo-section vacuum tube having a cathode common to both sections isused. The anode of the compensating section is energized from apotential divider and a control electrode common to both sections ofthis tubeis adjustably connected to the potential divider. A meter isconnected from a convenient point on the potential divider to the commoncathode and continuously indicates the condition of the tube. The meterreading may be corrected, at any time, by adjusting the position of theconnection of the control grid to the potential divider, withoutinterference with the operation of the working section of the tube. Byvirtue of the negative feed.- back from the anode-cathode circuit of thecompensating section to the control electrode common to both sections,automatic compensation for changes in emission will take place withinthe lim- 2 its of the available feedback in the compensating section.

In another embodiment of the invention, the two-section vacuum tube mayhave the shapeof a cathode ray tube, having a common source of.electrons, two anodes, and two control grids. The common source ofelectrons, a control grid and an anode form the working section,amplifying the applied signal voltages. The electron beam is oscillatedfrom anode to anode. The anode and control grid of the compensatingsection may be connected in the known manner, or to a potential divideras described above.

In the drawings:

Fig. 1 schematically shows a prior circuit;

Fig. 2 schematically shows one embodiment of the invention;

Fig. 3 schematically shows another embodiment of the invention;

Fig. 4 schematically shows another embodiment of the invention;

, Fig. 5 is a modification of Fig. 3; and

Fig. 6 is a modification of Fig. 4.

Fig. 1 discloses one stage of a compensated amplifier, of the type shownin United States Patent 2,308,997, January 19, 1943, S. E. Miller. Thespace discharge device I, comprises a cathode 2, which may be heated bythe usual heater (not shown). Opposite, or surrounding differentlongitudinal portions of the cathode 2 are the control electrodes orgrids 3, 5, and beyond or surrounding these grids are the anodes 4, 6.The anode a may be coupled to the input circuit of a succeedingamplifier by any suitable interstage coupling network, which may be, asshown, of the type disclosed in United States Patent 1,751,527, March25, 1930, H. Nyquist, comprising resistors .I, 8, 9, positive powersupply III and negative biasing power supply II. A'meter I6 may beconnected, as by a switch IT, or directly, to the output of-the present,or a succeeding stage of the amplifier. The common cathode 2 isconnected through a resistor, or other impedance, I8 to ground, and thepower supplies I0, I I. If the resultant voltage of the cathode 2 withrespect to ground produces an undesirably large bias of the grid 3, thismay be reduced by connecting the cathode 2 through a suitable resistorI9 to the negative power supply I I.

The voltages to be amplified are applied between terminal I2 connectedto the grid 3, and grounded terminal I3, and the amplified voltagesappear between terminals I4, I5.

The anode 6 is connected to ground through a positive power supply 20. Agrounded source of pensation for variations in the cathode activity isbased upon the assumption that the variations in cathode activity of thetwo portions of a cathode will be the same, but this assumption is notalways accurate, as the cathode activity may change over a small localarea, thus producing an erroneous compensation. In the vacuum tubesshown in Figs. 3 and 4, identically the same cathode, and electron beam,is used to activate both sections of the tube, thus, the compensationfor variations in cathode activity are always accu rate. r

In the systems shown in Figs. 1 and 3, the signals mustbe cut off, orreduced to zero, during an adjustment of the amplifier, thusinterrupting.

the use of the amplifier. In the systemsshown in Figs. 2 and 4 thisdisadvantage is avoided.

Elements having similar functions in Figs. 3 and 4 have the samereference numerals.

The cathode 32 is activated by the source 41; the electron beam iaccelerated by the anode polarized by the source so, and is oscillatedfrom anode 34 to anode 36 by the potentials impressed on the plates 53,5-?- by the oscillator 55. The anode 34 is coupled to the outputterminals 44, 45, by the resistor 31, 38, 39 and the sources 4%, 4|.

The signals are applied through the input termi-' nals 42, 43 to thecontrol electrode, or grid 33.

The anode 36 is connected through resistor 5'! to the source 40, andthrough the potential divider 58 to the grounded negative source ofpower- 59. The grid 35 is moved from the vicinity of anode 36 to aposition in which thi grid can control the density of the electron beamimpressed on both the anodes 34, 36- and is connected to one adjustabletap of potential divider 58. Capacitor 56 is connected from thisadjustable tap to ground. A meter Bil is connected from a secondadjustable tap of potential divider 58 to ground.

Initially, a meter is temporarily connected to the terminals 44, 45 andthe brush connected to grid 35 is adjusted until this meter indicates asuitable value for the output of the working section of the tube. Thebrush connected to meter 60 is adjusted until meter 60 indicate asuitable value, then the meter connected to terminals 44, 45 is removed.The brush connected to meter 60 may be adjusted so that the meter 6Gwill have a positive, or negative, or zero reading; but it is usuallymore convenient to use a center zero meter normally adjusted to readzero, 50 that the meter 60 will indicate deviations above and below thedesired value. The signals are applied to the terminals 42, 43, and theamplified signals taken off at the terminals 44, 45. If at any time thereading of meter 60 deviates from the desired value, the brush connectedto the grid 35 is adjusted to bring the indication of meter 69 back tothe desired value. This adjustment may be made while signals arebeingamplified, and does not materially affect the amplified signals.

While electrostatic plates 53, 54 have been 6" electron beam beingarranged to sweep over all the anodes in succession. The elements inFigs. 5 and 6, for input No. 1 and the control section, having the samefunctions as the corresponding elements in Figs. 3 and 4 have beendesignated by the same reference numerals. The elements in Figs. 5 and 6for input N0. 2, having the samefunctions as the corresponding elementsfor input No. l, have been designated by the same reference numeralsprimed. The operations of the devices shown in Figs. 5 and 6 will beobvious from the detailed descriptions of the operations of the devicesshown in Figs. 3 and 4. Thus one shown for oscillating the electronbeam, it is evident that other methods, such as magnetic coils, may beused for this purpose.

While only a single working anode 34 is shown in Figs. 3 and 4, it isevident that a plurality of such anodes, and their associated grids, maybe included with the compensating anode in a single tube, as shownrespectively in Figs. 5 and 6, the.

tions of several different amplifiers. In thi case,-

the integrated current drawn by the auxiliary anode is preferably notless than the sum of the currents drawn by all the working anodes.

' What is claimed is:

1, An electronic translating circuit including means for producing anelectronic beam, one or more working anodes, an auxiliary anode, meansfor recurrently sweeping said beam across all said anodes, a controlelectrode individual to each said working anode, input circuitsindividually connected to said beam producing means and said controlelectrodes, output circuits individually connected to said beamproducing means and said working anodes, an auxiliary control electrodeassociated with said auxiliary anode to control the density of theelectronic beam drawn to said working anodes, and means for adjustablybiasing said auxiliary control electrode.

2. An electronic amplifying circuit including means for producing anelectronic beam, an impedance connected to said means, one or moreworking anodes, an auxiliary anode, means for recurrently sweeping saidbeam across all said anodes, a control electrode individual to each saidworking anode, input circuits individually connected to said impedanceand said control electrodes, output circuits individually connected tosaid impedance and said working anodes, a source of power connectedbetween said impedance and said auxiliary anode, an auxiliary electrodeassociated with said auxiliary anode to control the density of theelectronic beam drawn by said source through said impedance, and meansfor adjustably biasing said auxiliary electrode.

3. The combination in claim 2 in which said impedance comprises aresistor connected in parallel with a capacitor.

4. An electronic amplifying circuit including means for producing anelectronic beam, one or more working anodes, an auxiliary anode, meansfor recurrently sweeping said beam across all said anodes, a controlelectrode individual to each said working anode, inputcircuitsindividually connected to said beam producing means and said controlelectrodes, output circuits individually connected to said beam producinmeans and said working anodes, an auxiliary electrode arranged tocontrol the density of said beam, a source of power connected to saidauxiliary anode, means for indicating the current flowing from saidauxiliary anode and means for adjustably biasing said auxiliaryelectrode in accordance with said indications.

5. The combination in claim 4 in which said auxiliary anode is connectedthrough a first resistor to a grounded positive source of power andthrough a second resistor to a grounded negative source of power, saidauxiliary electrode is connected to a first tap in said second resistor,and

amn on a meter is. connectedfrorn: groundto a secondeam said secondresistor.

6; An electronic amplifyi g circuit including" one: or; more; working.anodes, an auxiliary anode.

amactivated cathode common-to all said anodes,

3;. control, electrode, individual to each workinganode; input circuitsindividuall connectedv to said control; electrodes and said cathode,output. circuits, individually: connected to said working anodes, andsaid cathode, an auxiliary control. electrode, common to allsaid anodes,a first resistor-and a-positive sourceof power connecting said auxiliaryanodeto said cathode, a second resistor andanegative-sourcc of powerconnecting said auxiliary anode to, said cathode, a first tapinsaidisecond resistor. connected to said auxiliary control electrode, andameter connectedfrom asecond tap in said second resistor to saidcathode.

7. An electronic amplifying circuit including one'or; more working;anodes, a control electrode individual, to each working anode, anactivated,

cathode common to all said anodes, input circuits individuallyconnectedto eachcontrol, elec.

trode and said cathode, output circuits individually connected to eachworking anode and said cathode, an auxiliary. anode, a source, of

POW d. an impedance. connected serial re lationship from said auxiliaryanode to said catty,

ode, said auxiliary anodebcing, so located-wit respect to said controlelectrodes thatthe electron; flow from said cathodelto said auxiliaryanoderis; independent, of the: potentials, on said, control electrodes,and an auxiliary control electrode com-l monto all said anodes andadjustably 001111801 851 tosaid impedance.

8. The combination in claim 7 with. a, meter connected to said impedanceto indicate, the. changesin the current toaid-auxiliary anode.

A'IETELL B; ANDERSON;

REFERENCES CITED The following references are of record in thefilelofvthis patentr UNITED STATES PATENTS Number. Name Date--2,107,410, Dreyer s,,., c -s Feb. 8,1933 2,308,997 Jan..,19, 19432,354,718 Tuttle l Aug, 1, 1944 2,392,415 Soller, -F" an! 8, 9.462,399,441 Krebs F,. .,Apr. 30,1946

